This is a tough boxed set of cut-outs to find. Add that to it being complete and in near-mint condition, I am not surprised it brought a strong price. Dennison first issued this set in 1924 with a stock number of H101.
Unfortunately, whomever the buyer was bought newly made items with no collectible value. The sad thing is that this seller was informed by a long-time collector in Pennsylvania that she was selling newly made items and mightily resisted this information. (I experience this phenomenon all the time, sadly...) Be sure to do your research before buying vintage Halloween memorabilia. Prices are high enough across the board that a little bit of time invested in education in our fun hobby will surely prevent you from buying such things.